Canyon (CivBE)

Canyons are deep chasms in the surface of this alien planet, impossible for non-flying units to move across. They’re not particularly helpful to a city, except as barriers to approach, although certain buildings may improve their yield.
Canyons are impassable terrain for all but hovering units. Geothermal resources are sometime found near, and the Tectonic Anvil Wonder requires proximity to a Canyon.